LTE makes headway on global roaming, speed and voice

LTE is simultaneously being pushed forward on several fronts, and the result for users will be faster networks, better coverage and the ability to access networks while travelling abroad.

LTE has now become a mainstream technology with major deployments in every geographical area. But the abbreviation stands for Long-Term Evolution and what has been available so far in terms of speeds and features is only the beginning, a fact highlighted over the last week as operators and vendors have announced the groundwork for new improvements.

There are commercial LTE networks in 70 countries, and by the end of the year that number will have increased to 87, according to the Global Mobile Suppliers Association (GSA). Most of those LTE customers cannot yet use their LTE-enabled devices abroad, but that is slowly starting to change. The rise in the number of networks, and the availability of smartphones with up to six LTE spectrum bands, is making it viable.

Swisscom's LTE subscribers have, for example, been able to surf when visiting South Korea since June 21. The coverage is expected to be expanded to Canada and Hong Kong at the beginning of next month, and become available in some European countries late this summer. More countries will then be added on an ongoing basis, the Swiss operator said.

The global nature of Swisscom's LTE roaming offering makes it an important step, according to Ericsson, which has provided the underlying equipment. It shows that Diameter, the signalling protocol that makes LTE roaming possible, has become more mature, and roaming is now more about operators sitting down and signing agreements. Other operators that offer roaming on a more regional basis include TeliaSonera and Telstra.

While many operators are busy rolling out first generation LTE, SK Telecom on Wednesday bragged that it had launched the world's first publicly available LTE-Advanced network with the world's first compatible phone, Samsung Electronics' Galaxy S4 LTE-A. Another Korean operator, LG U+, will start offering LTE-Advanced in July, it said on Thursday.

LTE-Advanced includes a number of new technologies, and of those SK has decided to implement two elements, Coordinated Multi-Point (CoMP) and Carrier Aggregation. The latter will soon become available in other parts of the world, as well.

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Carrier Aggregation allows networks to devote more resources to some users by treating two channels in the same or different frequency bands as if they were one. That technique will allow SK Telecom to offer speeds of up to 150Mbps by combining two 10MHz channels. That speed can be achieved without Carrier Aggregation by operators who have 20MHz of continuous spectrum in one band, which is kinder on smartphone and tablet batteries.

"It is true that Carrier Aggregation uses more battery, but what you can do is use clever algorithms to carefully choose when to turn it on," Narvinger said.

The advantages of using Carrier Aggregation will instead become more apparent when operators combine larger chunks of spectrum. Speeds of up to 300Mbps will be possible by marrying two 20MHz channels. The current standards allow for up to five 20 MHz channels to be aggregated. according to SK.

But Carrier Aggregation isn't just about theoretical top speeds: Implementing the technology will also mean improved (albeit lower) speeds even for users who haven't got the perfect coverage needed for the highest speeds, according to Narvinger.

CoMP, the other LTE-Advanced technology adopted by SK Telecom, is used to coordinate and combine signals from multiple base stations to improve both coverage and capacity, especially at the edge of a base station's coverage area. It can be used to improve uplink and downlink quality.

Next year, SK Telecom also plans to add Enhanced Inter-cell Interference Coordination (eICIC), which ensures that signal quality isn't degraded because of interference from a different base station than the one the user is attached to.

The technology can be particularly important when building so-called heterogeneous networks, which use a mixture of traditional large base stations, called macro cells, and smaller base stations to provide additional coverage at busy spots within the macro cells.

Adding small base stations to a network should result in better coverage and higher speeds overall, but it also makes interference more difficult to control. That's where eICIC comes in: Using it decreases interference for users attached to the small cell, at the expense of reducing macro cell capacity. For the technology to make sense, between 60 percent and 80 percent of the traffic has to go via the small cells, according to Narvinger.

A number of other operators including Sprint in the U.S., Telstra in Australia, Optimus in Portugal, Yota in Russia, and Tele2 and Telenor in Sweden have all announced LTE-Advanced trials or roll-out plans, according to GSA. Verizon Wireless plans to start using Carrier Aggregation during the second half of the year, according to spokesman Tom Pica.

LTE has very much been developed with data in mind, but most operators are still dependent on voice revenue, and vendors are making progress here too.

Sony's Xperia SP M35t phone supports TDD and FDD versions of LTE, as well as TD-SCDMA, HSPA and GSM. Sony announced the smartphone this week and will begin selling it when 4G licenses are finally awarded in China, something that is expected to happen this year.

This is the first time a commercial 4G phone has been used to show HD voice over TD-LTE, and it marks a key milestone in the maturity of the TD-LTE ecosystem, according to Ericsson.

TD-LTE uses one channel for both upload and download traffic, compared to LTE-FDD, which uses separate channels for download and upload traffic. Calls can now be made on the two network types and between them, as well.

"We strongly believe that FDD and TDD will grow together into one network," Narvinger said.

Voice over LTE (VoLTE) has so far seen little success, and has only been rolled out by a small number of operators. But Narvinger thinks that successful launches in South Korea will help increase its popularity.

"That has shown it works well, and that has increased interest globally," he said.

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